1. Field of the Invention
The present invention relates to a control system of an automatic transmission and, more particularly, to a control system of an automatic transmission for an automotive vehicle, particularly an automatic transmission with a main transmission and an auxiliary transmission, so adapted as to improve the prevention of a shift shock of the vehicle by enabling a stable control of the automatic transmission by implementing both of a feedback control and a learning control at the time of a transition of a shift of both of the main transmission and the auxiliary transmission.
2. Description of the Related Art
Recently, an automatic transmission for an automotive vehicle, having a main transmission and an auxiliary transmission connected with the main transmission, has been proposed and are being developed for commercialization, the automatic transmission being provided with five forward speed stages and one rearward speed stage. For the automatic transmission with the main transmission and the auxiliary transmission, however, it is extremely difficult to control a shift to be made by the main transmission simultaneously with the auxiliary transmission. A shift shook may be caused to occur unless a shift between the coupling of friction coupling elements of both of the main transmission and the auxiliary transmission and the releasing of the coupling therebetween be performed in an appropriate way, i.e. unless the pressure for coupling the friction coupling elements and the pressure for releasing the coupling thereof are controlled appropriately.
Japanese Patent Unexamined Publication (kokai) No. 62-4,950 discloses technology that involves preventing a shift shock by starting the shift of the main transmission prior to the shift of the auxiliary transmission and, at the same time, synchronizing the shift of the main transmission with that of the auxiliary transmission at the time of the end of the shift.
Japanese Patent Examined Publication (kokoku) No. 63-3,183 discloses a control system for compensating for a line pressure, which is so adapted as to control the line pressure of the automatic transmission by performing a learning control on the basis of a deviation between a target shift time and an actual shift time in implementing the shift of the automatic transmission.
When the main transmission and the auxiliary transmission of the automatic transmission are shifted simultaneously, it is necessary to couple one or more friction coupling elements and to release the coupling of the plural friction coupling elements; however, a shift shock may be caused to occur one or plural times if the control of the pressure for coupling or releasing the coupling of the friction coupling element and elements would not be appropriate.
A control system for an automatic transmission is being developed, which is so adapted as to control the coupling pressure of the friction coupling elements to set a target gear ratio progress value to a predetermined value on the basis of a gear ratio progress value of the main transmission and a gear ratio progress value of the auxiliary transmission, when the main transmission and the auxiliary transmission are shifted simultaneously. The control system of this kind is arranged to control an actual shift progress state, i.e. a state in which an actual shift progresses, so as to follow a target value preset by using the gear ratio progress value of the main transmission and the gear ratio progress value of the auxiliary transmission as parameters, the gear ratio progress values being determined on a real time. However, the shift control cannot be achieved with high and stable responsiveness unless parameters such as abrasion of abrasive materials for the friction coupling elements of the transmissions, oil temperature, changes in characteristics of operating oil, abrasion of gears, engine load, outside air temperature, and so on, be taken into account, because these parameters may affect the shift control.
The technology as disclosed in Japanese Patent Laid-open Publication No. 62-4,950 cannot solve the problems as have described hereinabove, because it relates to the adjustment of the shift timing of the main transmission and the shift timing of the auxiliary transmission. On the other hand, the technology as disclosed in Japanese Patent Laid-open Publication No. 63-3,183 is involved with the adjustment of the line pressure and it cannot be applied directly to the shift control at the time of transition of the automatic transmission with both of the main transmission and the auxiliary transmission.